In urban and suburban areas, public transport is very often provided by urban buses propelled by conventional engines, which are usually diesel engines that employ a heterogeneous mixture, e.g., diesel fuel, which are particularly polluting. Attempts at making these vehicles run on fuels said to be less polluting (LPG, etc.) have been made, but the results in terms of pollution are particularly weak.
A method for reducing pollution of an engine with an independent external combustion chamber, has described, in the inventor's French patent application, recorded under national record number 95/02838, in which method, the air-fuel mixture is drawn into and compressed in an independent intake and compression chamber then transferred (still under pressure) into the independent combustion chamber to be ignited therein, either using a spark in the case of an engine with a homogenous mixture, or by self-ignition in the case of a diesel engine with a heterogeneous mixture, in order to increase the temperature and pressure of the said mixture which, following the opening of a transfer connecting the said independent combustion chamber to an expansion and exhaust chamber (it too independent), will be expanded in the latter chamber in order to produce work therein, then exhausted to the atmosphere through an exhaust pipe, in which method, when operating in town (or at low power), the fuel injector is no longer operated and, in this case, there is introduced into the combustion chamber, somewhat after the fuel-free compressed air from the intake and compression chamber has been let into the latter, a small amount of additional compressed air from an external reservoir where the compressed air is stored at very high pressure. This small amount of compressed air at ambient temperature will heat up upon contact with the mass of hot air contained in the combustion chamber, and will expand so as to increase the pressure in the combustion chamber to allow work to be delivered during expansion. This engine thus employs a dual-mode or dual-energy operation.
There is a need for an engine, especially for the urban markets, that use less fuel and aid in reducing the pollution caused by other vehicles using conventional internal combustion engines.